It is known that some projectors that project and display images use respective laser light sources of red (R), green (G) and blue (B), for example, to form image light. If the light output characteristics of a laser light source are degraded due to aging deterioration or temperature change of a laser element, for example, a luminance ratio among respective light beams in R, G and B may be changed while representation is shown in white, leading to a problem of fluctuations in white balance. Thus, in order to keep white balance properly, correction has been required in response to change of light output characteristics.
According to known technique relating to white balance correction, with respect to a light source deteriorated most seriously, light output from a remaining light source is made to agree with light output from the light source deteriorated most seriously to reduce luminance as a whole, thereby keeping white balance constant (Japanese Patent Application Laid-Open No. 2007-65574).
According to known technique employed to control the temperature of a laser light source, light output from the laser light source is reduced if the operating rate of a Peltier element unit for cooling the laser light source reaches a predetermined value, thereby suppressing temperature increase of the laser light source (Japanese Patent Application Laid-Open No. 2011-191526).
The aforementioned technique described in Japanese Patent Application Laid-Open No. 2007-65574 is employed to correct the white balance of a projector that uses a single laser light source as a light source for each of R, G and B. Thus, this conventional technique cannot be employed to correct the white balance of a projector that uses a plurality of laser light sources as light sources for each of a plurality of colors.